Chalcopyrite compounds, particularly deselinized copper and indium CuInSe2, also called CIS, and its alloys with gallium (“CIGS”) and sulfur (CIGSS) are promising candidates when used as a light-absorbing layer in photovoltaic cells in thin films. U.S. Pat. No. 4,335,266 is one example that describes the technology of CIS cells. Because of their high coefficient of absorption, a 1 to 2 micrometer thickness of CIGS chalcopyrite is sufficient to absorb all incident light. By changing the ratio of In/Ga and Se/S, a large range of values (1 to 2.4 eV) for the energy gap (“band-gap”) can be obtained, and structures with a gradual band-gap are used in high output photovoltaic cells. Solar cells possessing a layer of polycrystalline CIGS have demonstrated conversion outputs exceeding 19%, as described by K. Ramanathan et al., Photovoltaics, 2003, 11, p. 225. The first industries have emerged and their production of solar cells with thin CIGS films is based on co-evaporation and selenization methods requiring a high vacuum, as described by Powalla et al., Proceedings of the 3rd WCPEC, Osaka, Japan, 2003, in publication, and by Kushiya et al. Proceedings of the 3rd WCPEC, Osaka, Japan, 2003. Current CIGS solar modules have average outputs of 10 to 13%, with the goal being to obtain 13 to 15% with lower production costs than with crystalline silicon. These high output CIGS modules are obtained with expensive vacuumized equipment and sophisticated method controls; furthermore, from 20 to 40% of the primary materials are inevitably wasted. In order to reduce manufacturing costs, alternative deposition methods based on methods that do not rely on high vacuums have been proposed and studied. In general, these methods should allow the CIGS chalcopyrite layer to be quickly and simply deposited while completely using up the primary materials such as indium and gallium, which are relatively rare and expensive elements. Aside from the well-known methods such as electrochemical procedures, see for example U.S. Pat. No. 5,871,630 and pyrolysis by spraying, for example, as in U.S. Pat. Nos. 4,242,374 or 6,379,635, methods based on deposition of a paste have attracted attention these last few years, since outputs in excess of 13% have been obtained. As described in U.S. Pat. No. 6,127,202, Kapur et al. have developed a procedure where a paste containing nanocrystalline metal oxide powder is first deposited on a substrate by spreading it (“doctor-blade”), then a treatment in a hydrogen atmosphere allows the oxides to be reduced to a metal layer which is then heated in a diluted H2Se atmosphere. This method requires, first, the elaboration of nanometric metal oxide powders in the appropriate Cu/In and Cu/Ga ratio, and second, reduction in a hydrogenised atmosphere, followed by “selenization,” requiring at least two heated vacuum environments for safety, since the gas used, H2Se, is highly toxic, making the procedure costly. Furthermore, the fact that the deposition of metal oxide paste must be treated in two stages considerably lengthens the time required for the cycle to produce the thin film of chalcopyrite substrate.
In another procedure described in U.S. Pat. No. 5,910,336, organometallic compounds are dissolved in an organic solvent, then deposited on a substrate by spinning (“spin-coating”) or by plunging (“dip-coating”), and after pyrolysis in an inert or reductive atmosphere, the resulting metal alloy is selenized in an oven and the chalcopyrite layer thus formed is completed into solar cells with an output of up to 9%. This method also requires fairly toxic and expensive metal-organic precursors, and the two-step procedure (reduction and then selenization) adversely affects deposition speed and adds to the cost.